October, '14] ILLINGWORTH: TACHINID PARASITES 395 



to the liberations of the flies in the field. A field of ratoons was lo- 

 cated, which was well advanced and badly infested with borers. Fur- 

 thermore, the field was not to be cut for four or five months, in which 

 case the files would have opportunity to multiply greatly, and spread to 

 adjoining fields of j^oung cane which were already being infested by 

 the beetles. 



After six weeks, the parasitized canes were removed from the cages 

 and placed in the field in upright boxes (Plate 10, Fig. 2). In order to 

 protect these from ants, legs were attached and thej^ were placed in tins 

 of water. Exposure of the bare cane to the direct rays of the sun, at 

 noonday, would quickly kill the enclosed parasites, so we finally devel- 

 oped a method of tacking cocoanut leaves to the boxes, which proved 

 very satisfactory. 



A few of the canes were opened up to form an estimate of the number 

 of parasites: — 87 borer cocoons opened, showed 75 that were parasi- 

 tized — containing 172 fly puparia. This gave a result of 86 per cent 

 parasitized. 



During the second generation of the flies we put many more grubs 

 into the cages than in our first experiment. Then, by putting in fresh 

 cane and grubs daily, during the whole six weeks, we were able to more 

 than treble the results of the first generation. From a total of 4,354 

 borer grubs that were put into the two cages, a careful estimate made 

 by opening some of the canes as above, showed that we had fully 5,000 

 parasites developed. These were liberated in several fields of the 

 Nadi district, about 1,000 or more being put together in each place. 



Continuous Breeding 



Since soro.e of the flies of the second generation lived right through 

 the period of six weeks, it was decided to date the canes as they were 

 put into the cages each day, and remove them for the purpose of es- 

 tablishing colonies in the field at the end of about five weeks. By this 

 method of adding new artificially-infested canes daily, and keeping 

 always about 60 flies in each cage, we were able to remove 55 or 60 

 canes, containing fully 600 parasites, once a week. These parasitized 

 canes were shipped to various parts of Fiji, wherever borer-infested 

 fields were located. They were all exposed in upright boxes as shown 

 above. 



Enemies of the Tachinid Flies in the Field 



It seems wonderful that the files are able to reproduce at all in the 

 fields when we see all of the organisms that prey upon them. It is 

 only by their abundant powers of multiplication that they can over- 

 come these natural enemies; the principal difficulty is in getting a 



